From: Jingbo Xu Date: Fri, 7 Apr 2023 14:17:07 +0000 (+0800) Subject: erofs: introduce on-disk format for long xattr name prefixes X-Git-Tag: microblaze-v6.6~687^2~7 X-Git-Url: http://git.monstr.eu/?a=commitdiff_plain;h=b3bfcb9dbfff3da26a63efc60558acd60b96392a;p=linux-2.6-microblaze.git erofs: introduce on-disk format for long xattr name prefixes Besides the predefined xattr name prefixes, introduces long xattr name prefixes, which work similarly as the predefined name prefixes, except that they are user specified. It is especially useful for use cases together with overlayfs like Composefs model, which introduces diverse xattr values with only a few common xattr names (trusted.overlay.redirect, trusted.overlay.digest, and maybe more in the future). That makes the existing predefined prefixes ineffective in both image size and runtime performance. When a user specified long xattr name prefix is used, only the trailing part of the xattr name apart from the long xattr name prefix will be stored in erofs_xattr_entry.e_name. e_name is empty if the xattr name matches exactly as the long xattr name prefix. All long xattr prefixes are stored in the packed or meta inode, which depends if fragments feature is enabled or not. For each long xattr name prefix, the on-disk format is kept as the same as the unique metadata format: ALIGN({__le16 len, data}, 4), where len represents the total size of struct erofs_xattr_long_prefix, followed by data of struct erofs_xattr_long_prefix itself. Each erofs_xattr_long_prefix keeps predefined prefixes (base_index) and the remaining prefix string without the trailing '\0'. Two fields are introduced to the on-disk superblock, where xattr_prefix_count represents the total number of the long xattr name prefixes recorded, and xattr_prefix_start represents the start offset of recorded name prefixes in the packed/meta inode divided by 4. When referring to a long xattr name prefix, the highest bit (bit 7) of erofs_xattr_entry.e_name_index is set, while the lower bits (bit 0-6) as a whole represents the index of the referred long name prefix among all long xattr name prefixes. Signed-off-by: Jingbo Xu Reviewed-by: Gao Xiang Acked-by: Chao Yu Link: https://lore.kernel.org/r/20230407141710.113882-5-jefflexu@linux.alibaba.com Signed-off-by: Gao Xiang --- diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h index 1a4a614895c6..71a4b3c83132 100644 --- a/fs/erofs/erofs_fs.h +++ b/fs/erofs/erofs_fs.h @@ -76,7 +76,8 @@ struct erofs_super_block { __le16 extra_devices; /* # of devices besides the primary device */ __le16 devt_slotoff; /* startoff = devt_slotoff * devt_slotsize */ __u8 dirblkbits; /* directory block size in bit shift */ - __u8 reserved[5]; + __u8 xattr_prefix_count; /* # of long xattr name prefixes */ + __le32 xattr_prefix_start; /* start of long xattr prefixes */ __le64 packed_nid; /* nid of the special packed inode */ __u8 reserved2[24]; }; @@ -211,6 +212,13 @@ struct erofs_xattr_ibody_header { #define EROFS_XATTR_INDEX_LUSTRE 5 #define EROFS_XATTR_INDEX_SECURITY 6 +/* + * bit 7 of e_name_index is set when it refers to a long xattr name prefix, + * while the remained lower bits represent the index of the prefix. + */ +#define EROFS_XATTR_LONG_PREFIX 0x80 +#define EROFS_XATTR_LONG_PREFIX_MASK 0x7f + /* xattr entry (for both inline & shared xattrs) */ struct erofs_xattr_entry { __u8 e_name_len; /* length of name */ @@ -220,6 +228,12 @@ struct erofs_xattr_entry { char e_name[]; /* attribute name */ }; +/* long xattr name prefix */ +struct erofs_xattr_long_prefix { + __u8 base_index; /* short xattr name prefix index */ + char infix[]; /* infix apart from short prefix */ +}; + static inline unsigned int erofs_xattr_ibody_size(__le16 i_xattr_icount) { if (!i_xattr_icount)